Immunocytochemical localization of sphingolipid activator protein-1, the sulfatide/GM1 ganglioside activator, to lysosomes in human liver and colon.

Sphingolipid activator proteins (SAP) stimulate the enzymatic hydrolysis of sphingolipids. The results of biochemical studies have suggested that SAP are located within lysosomes. In this study we sought immunocytochemical verification of the lysosomal location of SAP-1, a SAP that stimulates the hydrolysis of sulfatide and GM1 ganglioside. We stained adjacent sections of normal adult liver and colon for either SAP-1, by peroxidase-labeled antibodies, or acid phosphatase, by enzyme histochemistry. At the light microscopic level, SAP-1 and acid phosphatase were present in similar cells of the colonic lamina propria and hepatic sinusoids, and in similar supranuclear sites of colonic epithelial cells. By electron microscopy, SAP-1 was present in vesicular structures morphologically similar to those containing acid phosphatase. Thus, SAP-1 is present in lysosomes of several different kinds of cells in the normal human liver and colon.